Ch 2 Light

Radio waves, visible light, and X-rays are all types of electromagnetic radiation.

True

The frequency of a water wave gives us its height.

False

If a new wave arrives on shore every two seconds, then its frequency is 2 Hz.

False

The greater the disturbance of the medium, the higher the amplitude of the wave.

True.

While gravity is always attractive, electromagnetic forces are always repulsive.

False

Changing the electric field will have no effect on the magnetic fields of a body.

False

As they move through space, the vibrating electrical and magnetic fields of a light wave must move perpendicular to each other.

True

Wave energy can only be transmitted through a material medium.

False

As white light passes through a prism, the red (longer) wavelengths bend less than the blue (shorter) wavelengths, so forming the rainbow of colors.

True

Observations in the X-ray portion of the spectrum are routinely done from the surface of the Earth.

False; X-rays are absorbed by the atmosphere.

In blackbody radiation, the energy is radiated uniformly in every region of the spectrum, so the radiating body appears black in color.

False

According to Wien’s law, the larger the blackbody, the shorter its peak wavelength.

False

A blue star has a higher surface temperature than a red star.

True

According to Wein’s law, the higher the surface temperature of a star, the redder its color.

False

Doubling the temperature of a blackbody will double the total energy it radiates.

False

As a star’s temperature increases, the frequency of peak emission also increases.

True

The spectral lines of each element are distinctive to that element, whether we are looking at emission or absorption lines.

True

An absorption line spectrum, with dark lines crossing the rainbow of the continuum, is produced by a low-density hot gas.

False

An emission line results from an electron falling from a higher to lower energy orbital around its atomic nucleus.

True

The shorter a wave’s wavelength, the greater its energy.

True

Spectral lines are produced when an electron makes a transition from one energy state to another.

True

In the Bohr model of the atom, an electron can only exist in specific, well-defined energy levels.

True

When an electron in a hydrogen atom drops from the second to the first excited energy state it emits a bright red emission line called hydrogen alpha.

True

The Zeeman effect reveals the presence of strong magnetic fields by the splitting of spectral lines.

True

The broader the spectral line, the higher the pressure of the gas that is creating it.

True

In the Doppler effect, a red shift of spectral lines shows us the source is receding from us.

True

The larger the red shift, the faster the distant galaxy is rushing toward us.

False

If a fire truck’s siren is rising in pitch, it must be approaching us.

True

You would perceive a change in a visible light wave’s amplitude as a change in its color.

False

Spectroscopy of a star can reveal its temperature, composition, and line-of-sight motion.

True

The Doppler effect can reveal the rotation speed of a star by the splitting of the spectral lines.

False

Which of these is not a form of electromagnetic radiation?
A) light from your camp fire
B) ultraviolet causing a suntan
C) DC current from your car battery
D) radio signals
E) X-rays in the doctor’s office

C

Consider this diagram. Which statement is true?
Refer to drawing.
A) The amplitude is 6 and the wavelength is 4.
B) The amplitude is 8 and the wavelength is 6.
C) The amplitude is 4 and the wavelength is 12.
D) The amplitude is 4 and the wavelength is 6.
E) The amplitude is 8 and the wavelength is 12.

D

A wave’s velocity is the product of the
A) frequency times the period of the wave.
B) amplitude times the wavelength of the wave.
C) amplitude times the frequency of the wave.
D) frequency times the wavelength of the wave.
E) period times the energy of the wave.

D

If a wave’s frequency doubles and its speed stays constant, its wavelength
A) becomes 16× longer.
B) is unchanged, as c is constant.
C) is also doubled.
D) is now 4× longer.
E) is halved.

E

The speed of light in a vacuum is
A) 768 km/hour.
B) 300,000 km/sec.
C) 186,000 miles per hour.
D) not given.
E) h = E/c.

B

Which of these is the same for all forms of electromagnetic (E-M) radiation in a vacuum?
A) frequency
B) photon energy
C) wavelength
D) amplitude
E) speed

E

The two forms of electromagnetic (E-M) radiation that experience the least atmospheric opacity are
A) X and gamma radiation.
B) ultraviolet and infrared waves.
C) visible light and radio waves.
D) microwaves and radio waves.
E) visible light and infrared waves.

E

The radiation our eyes are most sensitive to is the color
A) violet at 7,000 Angstroms.
B) blue at 4,321 nm.
C) black at 227 nm.
D) yellow-green at about 550 nm.
E) red at 6563 Angstroms.

D

Medium A blocks more of a certain wavelength of radiation than medium B. Medium A has a higher
A) transparency.
B) albedo.
C) opacity.
D) seeing.
E) clarity.

C

In the Kelvin scale, absolute zero lies at
A) 273 degrees C
B) -373 degrees C.
C) zero K.
D) Both A and B are correct.
E) Both A and C are correct.

.C

What is true of a blackbody?
A) It appears black to us, regardless of its temperature.
B) It has a complete absence of thermal energy.
C) If its temperature doubled, the peak in its radiation curve would be doubled in wavelength.
D) Its energy is not a continuum.
E) Its energy peaks at the wavelength determined by its temperature.

E

What is the name of the temperature scale that places zero at the point where all atomic and molecular motion ceases?
A) Ransom
B) Celsius
C) Centigrade
D) Fahrenheit
E) Kelvin

E

The total energy radiated by a blackbody depends on
A) the fourth root of its temperature.
B) the fourth power of its temperature.
C) the cube of its temperature.
D) the square of its temperature.
E) the square root of its temperature.

B

Increasing the temperature of a blackbody by a factor of 3 will increase its energy by a factor of
A) 9
B) 3
C) 81
D) 6
E) 12

C

If a star was the same size as our Sun, but was 81times more luminous, it must be
A) nine times hotter than the Sun.
B) twice as hot as our Sun.
C) 81 times hotter than the Sun.
D) three times hotter than the Sun.
E) four times hotter than the Sun

E

The Sun’s observed spectrum is
A) a continuum with absorption lines.
B) a continuum with emission lines.
C) only emission lines on a black background.
D) a continuum with no lines, as shown by the rainbow.
E) only absorption lines on a black background.

A

The element first found in the Sun’s spectrum, then on Earth 30 years later, is
A) solarium.
B) aluminum.
C) helium
D) hydrogen.
E) technicum.

C

A jar filled with gas is placed directly in front of a second jar filled with gas. Using a spectroscope to look at one jar through the other you observe dark spectral lines. The jar closest to you contains
A) the cooler gas.
B) the exact same gas as the other jar.
C) gas at very high pressure.
D) the hotter gas.
E) gas at the same temperature as the other jar.

A

Which of these is emitted when an electron falls from a higher to lower orbital?
A) another electron
B) a positron
C) a photon
D) a graviton
E) a neutrino

C

In Bohr’s model of the atom, electrons
A) are spread uniformly through a large, positive mass.
B) move from one orbit to the next orbit in many small steps.
C) are not confined to specific orbits.
D) can be halfway between orbits.
E) only make transitions between orbits of specific energies.

E

In general, the spectral lines of molecules are
A) the same as the atoms they contain.
B) more complex than those of atoms.
C) only absorption lines.
D) less complex than those of atoms.
E) nonexistent.

B

Electromagnetic radiation
A) has only the properties of waves.
B) can only travel in a dense medium.
C) has nothing in common with radio waves.
D) is the same as a sound wave.
E) can behave both as a wave and as a particle.

E

In a hydrogen atom, a transition from the 2nd to the 1st excited state will produce
A) the bright red Balmer alpha emission line.
B) a dark absorption line.
C) no emission line.
D) three different emission lines.
E) an ultraviolet spectral line.

A

For hydrogen, the transition from the first to third excited state produces
A) a red emission line.
B) an infrared line.
C) a blue green absorption line.
D) an ultraviolet line.
E) a violet emission line.

C

The observed spectral lines of a star are all shifted towards the red end of the spectrum. Which statement is true?
A) The second law of Kirchhoff explains this.
B) The star is not rotating.
C) The star has a radial velocity towards us.
D) This is an example of the photoelectric effect.
E) This is an example of the Doppler effect.

E

If a source of light is approaching us at 3,000 km/sec, then all its waves are
A) red shifted out of the visible into the infrared.
B) blue shifted by 1%.
C) not affected, as c is constant regardless of the direction of motion.
D) blue shifted out of the visible spectrum into the ultraviolet.
E) red shifted by 1%.

B

If the rest wavelength of a certain line is 600 nm, but we observe it at 594 nm, then
A) the source is approaching us at 0.1% of the speed of light.
B) the source is approaching us at 1% of the speed of light.
C) the source is receding from us at 10% of the speed of light.
D) the source is getting 1% hotter as we watch.
E) the source is spinning very rapidly, at 1% of the speed of light.

B

According to the Zeeman effect, the splitting of a sunspot’s spectral lines is due to
A) a Doppler shift.
B) temperature variations.
C) their magnetic fields.
D) their radial velocity.
E) their rapid rotation.

C

The distance from a wave’s crest to its undisturbed position is the ________.

amplitude

The product of the wavelength times the frequency of a wave is its ________.

velocity

A wave with a period of .01 seconds has a frequency of ________ Hz.

100 Hz

A frequency of one hundred ________ means the wave is vibrating one hundred million times per second; this is a typical carrier frequency for FM (frequency modulation) radio.

Mega Hertz (MHz)

A wave with a frequency of 2 Hz will have a period of ________.

0.5 s

An FM station broadcasts at a frequency of 100 MHz. The wavelength of its carrier wave is ________.

3 meters

In electromagnetic waves, the electric and magnetic fields vibrate ________ to each other.

perpendicular

A featureless spectrum, such as a rainbow, is said to be ________.

continuous

Stars that appear blue or white in color are ________ than our yellow Sun.

hotter

According to Wein’s law, the wavelength of the peak energy will be ________ if the temperature of the blackbody is doubled.

halved

The Sun’s blackbody curve peaks in the ________ portion of the spectrum.

visible

Knowing the peak emission wavelength of a blackbody allows you to determine its ________.

temperature

Stefan’s law notes that total energy radiated is proportional to the ________ power of the temperature of the blackbody.

fourth

A dense, hot body will give off a(n) ________ spectrum.

continuous

Fraunhofer was the German astronomer who first noted ________ lines in the Sun’s spectrum.

absorption

The common element with bright red, blue-green, and violet emission lines is ________.

hydrogen

The common element discovered in the Sun’s spectrum before it was found here is ________.

helium

When an electron moves from a lower to a higher energy state, a photon is ________.

absorbed

An electron has a ________ electric charge.

negative

The most energetic photons are ________.

gamma rays

The energy of the photon depends on its ________.

wavelength or frequency